PROJECT SUMMARY: Global chromatin reorganization and epigenetic changes govern the amazing ability of hematopoietic stem cells to generate vastly different blood cell types. This control is achieved by gene level changes to chromatin accessibility, controlled by the deposition of histone tail modifications that can either signal to condense a region into heterochromatin, restricting access by transcription machinery and thereby ?silencing? a gene; or by performing the reciprocal function, relaxing the chromatin and making the DNA more accessible to transcription machinery. Disruptions of these processes can cause gene dysregulation driving lineage commitment and therefore cause disease. We seek to determine the underlying mechanisms during hematopoiesis that control chromatin accessibility and gene localization that drive lineage commitment. The long-term goal of my project is to determine the temporal dynamics of chromatin condensation and localization during blood cell differentiation. Previous work in the lab has shown the ratio of heterochromatin to euchromatin increases as cells differentiate from embryonic stems cells to hematopoietic stem cells to mature blood lineages. However, the global levels of histone modifications did not change. In addition, H3K9me3, a known heterochromatin mark, becomes localized towards the periphery of the nucleus during differentiation. These findings have led us to hypothesize that normal blood differentiation requires silencing of pluripotency genes and alternative lineage drivers by condensation into heterochromatin and sequestration to the nuclear lamina. We will test this hypothesis by the following aims: Aim 1 will investigate how chromatin accessibility and nuclear localization dynamics of genes throughout hematopoiesis affect lineage commitment, Aim 2 will determine the function of chromatin localization to Lamin B1 and cis element accessibility during hematopoietic stem cell differentiation. Completion of these aims will illuminate the epigenetic mechanisms that govern lineage fate decisions in hematopoiesis. This knowledge can be leveraged to improve maintenance and expansion of HSCs in culture for cell-replacement therapies and design strategies for preventing aberrant differentiation in hematopoietic disorders and cancers.